Unity is a shell interface for the GNOME environment used primarily on Ubuntu systems. It was designed to work well on small screens, for example, it employs a vertical application switcher. Unlike the other desktops/managers, it is not itself a collection of executables but uses existing applications.
If you have a machine running the Unity desktop, you can follow along with this section.
The following is a screenshot of Unity running on Ubuntu 12.04:
On the desktop is a GNOME terminal session and the Home folder. Starting with the vertical panel on the left is the Dash Home icon. It allows the user to find things quickly. Under that is the Home folder (already opened) and then the Firefox web browser. The next three are Libre Office Writer, Calculator, and Impress. Next is the Ubuntu Software Center, which is used to search for and purchase applications. The next icons are for Ubuntu One, a Terminal, System Settings, the Workspace Switcher, and the Trash folder.
To complete...